<h4>Tool</h4><table border="0"><tr><td valign="top"><b>Name</b></td><td valign="top">LS-Factor, Field Based</td></tr><tr><td valign="top"><b>ID</b></td><td valign="top">25</td></tr><tr><td valign="top"><b>Author</b></td><td valign="top">O.Conrad (c) 2013</td></tr><tr><td valign="top"><b>Specification</b></td><td valign="top">grid</td></tr></table><hr><h4>Description</h4>Calculation of slope length (LS) factor as used for the Universal Soil Loss Equation (USLE), based on slope and (specific) catchment area, latter as substitute for slope length. This tool takes only a Digital Elevation Model (DEM) as input and derives catchment areas according to Freeman (1991). Optionally field polygons can be supplied. Is this the case, calculations will be performed field by field, i.e. catchment area calculation is restricted to each field's area. 
References:

Boehner, J., Selige, T. (2006): Spatial Prediction of Soil Attributes Using Terrain Analysis and Climate Regionalisation. In: Boehner, J., McCloy, K.R., Strobl, J.: 'SAGA - Analysis and Modelling Applications', Goettinger Geographische Abhandlungen, 115, 13-27.

Desmet, P.J.J., Govers, G. (1996): A GIS Procedure for Automatically Calculating the USLE LS Factor on Topographically Complex Landscape Units. Journal of Soil and Water Conservation, 51(5), 427-433.

Freeman, G.T. (1991): Calculating catchment area with divergent flow based on a regular grid. Computers and Geosciences, 17:413-22

Kinnell, P.I.A. (2005): Alternative Approaches for Determining the USLE-M Slope Length Factor for Grid Cells. <a href="online">https://www.soils.org/publications/sssaj/abstracts/69/3/0674</a>

Moore, I.D., Grayson, R.B., Ladson, A.R. (1991): Digital terrain modelling: a review of hydrogical, geomorphological, and biological applications. Hydrological Processes, 5(1).

Moore, I.D., Nieber, J.L. (1991): Landscape assessment of soil erosion and nonpoint source pollution. J. Minnesota Acad. Sci., 55, 18-25.

Wischmeier, W.H., Smith, D.D. (1978): Predicting rainfall erosion losses - A guide to conservation planning. Agriculture Handbook No. 537: US Department of Agriculture, Washington DC.
<hr><h4>Parameters</h4><table border="1" width="100%" valign="top" cellpadding="5" rules="all"><tr><th>Name</th><th>Type</th><th>Identifier</th><th>Description</th><th>Constraints</th></tr>
<tr><th colspan="5">Input</th></tr><tr><td>Elevation </td><td>Grid (input)</td><td>DEM</td><td></td><td></td></tr><tr><td>Fields (*)</td><td>Shapes (optional input)</td><td>FIELDS</td><td></td><td></td></tr><tr><th colspan="5">Output</th></tr><tr><td>Field Statistics (*)</td><td>Shapes (optional output)</td><td>STATISTICS</td><td></td><td></td></tr><tr><td>Upslope Length Factor (*)</td><td>Grid (optional output)</td><td>UPSLOPE_AREA</td><td></td><td></td></tr><tr><td>Effective Flow Length (*)</td><td>Grid (optional output)</td><td>UPSLOPE_LENGTH</td><td></td><td></td></tr><tr><td>Upslope Slope (*)</td><td>Grid (optional output)</td><td>UPSLOPE_SLOPE</td><td></td><td></td></tr><tr><td>LS Factor</td><td>Grid (output)</td><td>LS_FACTOR</td><td></td><td></td></tr><tr><td>Sediment Balance (*)</td><td>Grid (optional output)</td><td>BALANCE</td><td></td><td></td></tr><tr><th colspan="5">Options</th></tr><tr><td>LS Calculation</td><td>Choice</td><td>METHOD</td><td></td><td>Available Choices:
[0] Moore & Nieber 1989
[1] Desmet & Govers 1996
[2] Wischmeier & Smith 1978
Default: 0</td></tr><tr><td>Type of Slope</td><td>Choice</td><td>METHOD_SLOPE</td><td></td><td>Available Choices:
[0] local slope
[1] distance weighted average catchment slope
Default: 0</td></tr><tr><td>Specific Catchment Area</td><td>Choice</td><td>METHOD_AREA</td><td></td><td>Available Choices:
[0] specific catchment area (contour length simply as cell size)
[1] specific catchment area (contour length dependent on aspect)
[2] catchment length (square root of catchment area)
[3] effective flow length
Default: 1</td></tr><tr><td>Stop at Edge</td><td>Boolean</td><td>STOP_AT_EDGE</td><td></td><td>Default: 1</td></tr><tr><td>Rill/Interrill Erosivity</td><td>Floating point</td><td>EROSIVITY</td><td></td><td>Minimum: 0.000000
Default: 1.000000</td></tr><tr><td>Stability</td><td>Choice</td><td>STABILITY</td><td></td><td>Available Choices:
[0] stable
[1] instable (thawing)
Default: 0</td></tr></table>(*) <i>optional</i>